As a press machine such as a transfer press for performing a plurality of pressing steps, there has been known a press machine that includes a workpiece transfer apparatus for sequentially transferring a workpiece to subsequent steps (e.g., see Patent Document 1). The work transfer apparatus of the press machine includes a workpiece holder for holding the workpiece to transfer, which is supported by a bar provided along the work transfer direction. When a die is replaced, the bar needs to be replaced such that the workpiece holder is replaced. For this purpose, the bar is formed by a fixed bar fixed within the press machine and a movable bar that is separable relative to the fixed bar. When the die is replaced, the movable bar, to which the workpiece holder is attached, is detached from the fixed bar to be placed on a moving bolster, and the workpiece holder is transferred to the outside of the press machine. The workpiece transfer apparatus includes a connecting device for connecting and separating the movable bar with and from the fixed bar.
The connecting device includes plate-like connecting portions provided both on mutually opposing ends of the movable bar and the fixed bar, and a hydraulic clamp is mounted on the connecting portion of the fixed bar. In the connecting portion of the movable bar, an engagement hole is provided to be engaged with the hydraulic clamp of the fixed bar. The hydraulic clamp, which downwardly protrudes form a lower surface of the connecting portion of the fixed bar, includes an engagement portion engaged with the engagement hole of the movable bar and a hydraulic device provided on the upper surface of the connecting portion of the fixed bar for moving the engagement portion in an up-and-down direction and rotating the engagement portion. The connecting portion of the fixed bar is brought into contact with the upper surface of the connecting portion of the movable bar while the fixed bar is moved in the up-and-down direction, and the engagement portion is hydraulically rotated after the engagement hole is penetrated by the engagement portion. While the engagement portion is in contact with the lower surface of the connecting portion of the movable bar, the movable bar is fixed to the fixed bar by pulling up the engagement portion. When the bar is detached in a die replacement operation, the engagement portion of the fixed bar is lifted down and rotated to be positioned to be engaged with the engagement hole, and subsequently the engagement portion is pulled out from the engagement hole by moving the fixed bar to the upper side, such that the movable bar is detached from the fixed bar.
In addition, in another connecting device, the fixed bar is moved relative to the movable bar in a longitudinal direction of the fixed bar, such that end surfaces of the bars are brought into contact to be connected with each other. For example, in a workpiece transfer apparatus where an entirety of the bar is movable in a feed direction (the longitudinal direction of the bar), the fixed bar of a feed drive mechanism side is moved by the feed drive mechanism. Since there is no feed drive mechanism provided for the fixed bar on the opposite side, a disconnecting device is provided for moving the fixed bar. The connecting device includes a claw that can be advanced and retraced in both sides of a direction perpendicular to the longitudinal direction of the bar. The claw is provided to the fixed bar. Further, the movable bar includes either a concave portion or a convex portion as an engagement portion with which the claw is engaged. When the movable bar is connected with the fixed bar, the claw is pressed against the movable bar to be engaged with the engagement portion. When the movable bar is separated from the fixed bar, the claw is moved away from the movable bar to be disengaged from the engagement portion.
[PATENT DOCUMENT 1] JP-A-2002-219535 (page 5)